1. Field of Endeavor
The present invention relates to the technology of gas turbines, to methods for operating a gas turbine, and to gas turbines useful for carrying out said methods.
2. Brief Description of the Related Art
When flue gas recirculation (FGR) is used in a gas turbine, i.e., a part of the flue gas at the exit of the gas turbine is recirculated back to the entrance and mixed with fresh gas (air), the O2 content is reduced, thereby limiting the operation due to incomplete combustion and resulting in high CO emissions.
Furthermore in the combustor of the gas turbine specific parts might be affected by rich and O2-depleted parts of the gas stream. Identifying this region and operating regimes is useful in operating the gas turbine in a safe mode ensuring long lifetime.
The control of the FGR ratio is a demanding task for the operation. For operating the engine, a measure of FGR ratio is needed. If not on mass flow directly, this could be done via the O2 content at the entrance of the compressor.
The use of O2 sensors for flame supervision has already been disclosed in the prior art (see document EP 2 107 305). The measurement of O2 concentrations in this document is limited to the determination of the flame temperatures (Tflame). Not mentioned is the application for FGR to prevent combustion regimes of rich stoichiometry.
It would be of great value to implement a fast, low cost and reliable sensor for measurement of the species concentration (particularly O2) at several points in the gas turbine and use these measurements for gas turbine control and/or optimization of the combustion performance.
With additional sensors the gas turbine would be enabled to approach the limits of operation.
For the combustor, the use of ZrO2 sensors could also be used locally to avoid lifetime reduction due to reducing atmospheres and to homogenize flames. Such ZrO2 sensors would be used similar to 3-way catalysts in cars for optimization of operation.